A new study, ‘Sedentary Behaviours, TV Viewing Time, and Risk of Young-Onset Colorectal Cancer,’ published in JNCI Cancer Spectrum, has identified a connection between prolonged time spent sitting while watching TV and increased risk of colorectal cancer for younger Americans. These findings are among the first to link specific sedentary behavioural patterns with risk of young-onset colorectal cancer.

Young-onset colorectal cancer, diagnosed under age 50, is increasing in the US and globally, sharply contrasting with the dramatic decreases among older people, largely as a result of cancer screening initiatives. Young-onset colorectal cancer has potentially different molecular characteristics compared to those of late-onset, and is typically more aggressive and found at a more advanced stage than those in older patients, resulting in greater years of life lost. Despite these trends, researchers have identified few risk factors specific to young-onset colorectal cancer.

Researchers here studied sedentary TV reviewing time, as well as other sedentary behaviours, in 89,278 American women in the Nurses' Health Study II. Of the 118 cases of young-onset colorectal cancer diagnosed over two decades of follow up, more than one hour of daily TV viewing time was associated with a 12% increase in risk compared to those who watched less.

The results were even more striking for those watching more than two hours/day with a nearly 70% increase in risk. This association was independent of BMI and exercise and was consistently observed among women without a family history of colorectal cancer. The association was also more pronounced for rectal cancer compared to colon cancer.

"This study may help identify those at high risk and who might benefit more from early screening," said Dr Yin Cao, Assistant Professor of Surgery at Washington University School of Medicine, and the study's co-senior author. "The fact that these results were independent of BMI and physical activity suggests that being sedentary may be an altogether distinct risk factor for young-onset colorectal cancer."